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Yellowstone Hot Spot Shreds Ancient Pacific Ocean : Discovery News
2/15/11 2:19 PM
Yellowstone Hot Spot Shreds Ancient Pacific Ocean
By Michael Reilly | Thu Sep 2, 2010 05:15 PM ET
If you thought the geysers and overblown threat of a supervolcanic eruption in Yellowstone
National Park were dramatic, you ain't seen nothing: deep beneath Earth's surface, the hot
spot that feeds the park has torn an entire tectonic plate in half.
The revelation comes from a new study in the journal Geophysical Research Letters that
peered into the mantle beneath the Pacific Northwest to see what happens when ancient
ocean crust from the Pacific Ocean runs headlong into a churning plume of ultra-hot mantle
material.
Geologically speaking, the Pacific Northwest is a peculiar place. Hot spots usually sit way out
on their own in the middle of a tectonic plate (think Hawaii or the Galapagos). Not Yellowstone
-- it pokes its way to the surface just a few hundred miles from the edge of the North America
plate, where a giant trench sends the Juan de Fuca tectonic plate sliding underneath
Washington, Oregon, and northern California.
Peering into the middle of this tectonic traffic jam is a tricky business. So scientists, led by
Mathias Obrebski of the University of California, Berkeley, had to build an image from seismic
waves bouncing around inside the mantle. What they found was a subterranean world filled
with violence.
The original data figures are a little hard to look at, but the team built a cartoon representation
of what they think is going on down there. Around 19 million years ago, the Yellowstone hot
spot first ascended from deep within the mantle. As it neared the surface, it ran into the
subducting Juan de Fuca plate.
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Yellowstone Hot Spot Shreds Ancient Pacific Ocean : Discovery News
2/15/11 2:19 PM
But the Juan de Fuca plate was itself young at the time (there's a mid-ocean ridge just off the
coast of Oregon that forms brand new crust to this day), so it hadn't had the chance fully
harden yet. When the crust and hot spot met, the hot mantle plume to found a weakness in the
plate -- perhaps a pre-existing fracture -- and punched a giant hole through it.
So, who cares? The encounter has had several amazing consequences. First, and most
obvious, it resurfaced much of northern Nevada, Idaho, and Wyoming over the last several
million years in basalt through a series of massive volcanic eruptions. Then there were the
tremendous supervolcanic explosions, which coated much of the western U.S. in thick
blankets of ash and made the Yellowstone park region what it is today.
Second, the team points out that the rise of the Yellowstone plume also coincided with a large
change in the rate at which the crust of the Pacific Ocean dives beneath North America. It's
possible that the shattered underlying plate simply didn't pull as much weight anymore, and the
subduction zone slowed down.
It's a new chapter in what we know about Yellowstone's legendary power to change the
landscape. Not only did its massive eruptions coat North America in ash from Idaho to the
Mississippi River, and south almost to the Gulf of Mexico, but its deep plume sent a ripple
effect through the very roots of the continent and the Pacific Ocean that fundamentally altered
the coastline of the Pacific Northwest.
Images: AGU
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